The war of words between Philippine President Rodrigo Duterte and the United Nations escalated on Thursday, with a UN envoy warning that “state actors” could be held responsible over hundreds of killings in a controversial anti-drug crackdown.

More than 1,500 people have died in Duterte’s fight against narcotics, police chief Director General Ronald de la Rosa told a Senate hearing, saying that 665 drug suspects were killed in “legitimate [police] operations” with another 889 were killed by vigilantes.

“Claims to fight illicit drug trade do not absolve the government from its international legal obligations and do not shield state actors or others from responsibility for illegal killings,” the UN Special Rapporteur on summary executions, Agnes Callamard said in a statement.

Claims to fight illicit drug trade do not absolve the government from its international legal obligations

Agnes Callamard, UN Special Rapporteur on summary executions,

The warning came a day after President Rodrigo Duterte, who swept to a landslide election victory in May largely on a pledge to kill thousands of criminals, called the UN “stupid” and vowed to continue his anti-narcotics offensive despite mounting criticism, including from UN chief Ban Ki-moon.

The UN statement, posted on the website of the UN High Commissioner for Human Rights, said Duterte had repeatedly urged police and the public to kill drug suspects, while promising to protect police from prosecution.

“Directives of this nature are irresponsible in the extreme and amount to incitement to violence and killing, a crime under international law,” Callamard said.

UN Special Rapporteur on the right to health, Dainius Puras, added that the fight against the illegal drugs trade must “respect the human rights of each person”.

On Wednesday, Duterte warned the UN not to meddle in the country’s politics and told foreign human rights watchdogs not to “investigate us as though we are criminals”.

UN Secretary-General Ban Ki-moon in June condemned Duterte’s apparent support for extrajudicial killings, saying they were “illegal and a breach of fundamental rights and freedoms”.

The UN’s anti-drugs office also this month said it was “greatly concerned” by the reports of extrajudicial killings.

But Duterte’s spokesman Martin Andanar said the public supported the crackdown.

“President Duterte has time and again warned us during the [election] campaign that if you vote for me, this is going to be bloody,” he said, adding that there is “no war without casualties”.